$DC04/56324/CIA1+4: Timer A Low-Byte (Kernal-IRQ, Tape)
Read : Get current value
Write: Set Low-Byte of value to count down from
Default Value: $25/37 on PAL
$95/149 on NTSC
Kernal-Reference:
STA $DC04 : $F907 $FDE4 $FDEE